Record reproducing system



y 1, 1945- c. M. SINNETT ET'AL I 2,374,785

RECORD REPRODUCING SYSTEM Filed Nov. 17, 1942 INVENTORS A'Ti'oRNEy Patented May 1, 1945 2,374,785 ancoan nnraonucmc SYSTEM Chester M. Sinnett, Westmont, and Rene Snepvangers, Haddon Heights, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application November 17, 1942, Serial No. 465,852

16 Claims.

Our present invention relates to sound record reproducers, and more particularly to a phonoraph system which does not employ a conventional form of tone arm. 7

In the past, sound records have been reproduced by placing the record on a motor-driven turntable, there being operatively associated with the turntable'an electrical pickup device supported by a so-called "tone arm. The pickup device is usually provided with a finely-pointed stylus, or needle, which rides in the record grooves. Various types of pickup devices have been used, viz; magnetic, crystal, capacity. Various elecelectrical voltage ouput of the pickup. For example, in a co-pending application of C. M. Sinnett (Serial No. 459,375, filed September 23, 1942) there is shown a system wherein the pickup device is capacitative, and acts to frequency modulate a high frequency oscillator in accordance with pickup capacity variations. In the Sinnett system the frequency modulated oscillations arev detected by a simple form of off-tune diode rectifier.

The design of the pickup support arm is complex. Typical arms are provided with two pivoting points. The entire mechanical system of the arm must be carefully designed, as thepickup must be supported without adding pressure on the groove. Furthermore, it is practically impossible to eliminate swinging and torsional tone arm resonances in conventional tone arms. Hence. elimination of the conventional form of pickup support arm would obviate the need for solving such mechanical design problems.

Accordingly, it is one of the main objects of our present invention to provide a phonograph record playback system wherein a "tone arm, or pickup support arm, is completely eliminated, and the pickup device of our invention being characterized by its being entirely supported by the record disc.

Another important object of our invention is to' improve phonograph record playback systems by eliminating the conventional form of tone arm, and employing an ultra-high frequency oscillator in a circuit for converting small capacity changes, corresponding to motional displacements of a stylus, into audio frequency voltages.

Yet another object of our invention is to provide record reproducing equipment which contrical networks have been used to amplify the 1 lines so that when the 'pickup'unit is placed on the record it functions in the normal manner to trace accurately the modulated record grooves.

Still other objects of our invention are to improve generally the simplicity and efliciency of pickup devices for phonograph record reproducer, apparatus, and more especially to provide such devices in a reliable and economical manner,

The novel features which we believe to be characteristic of our invention are. set forth with particularity in the appended claims; the invention itself, however, as to both its organization and method will best beunderstood by reference to the following description taken in connection with the drawing in which we have indicated diagrammatically a circuit organization whereby our invention may be carried into efiect.

In the drawing, wherein Fig. 1 shows the pickup device resting on the record prior to playing, and Fig. 2 shows in plan view the positioning of the pickup device upon rotation of the record, we have shown one embodiment of our invention wherein the usual and conventional motordriven turntable is schematically represented. On the turntable is shown a phonograph record I of any customary typ the manner of cutting of the record grooves is not important to the present invention. The pickup itself may be of any well known type. Where the electrical voltage, provided by the mechanical motion of the finely-pointed stylus riding in the record groove,

is to be amplified by the use of the aforementioned Sinnett system, the pickup device may be of the capacity type. Of course, the pickup may be of the magnetic or crystal types if desired. In the latter case the pickup output could feed directly into a normal audio amplification system.

In the present application let it be assumed that the pickup unit isdesignated schematically by numeral 2; and that it is inserted within a circular opening provided in the support 3. The

. pickup unit 2 may be constructed in accordance sists essentially of a, pickup and supporting means connected with a voltage utilizing network by means of a pair of twisted transmission lines whereby the pickup is-limited in motion by the with the teachings of QM. Sinnett in application Serial No. 414,305, filed October 9, 1941. eral, such a pickup unit consists of a finely-pointed stylus, or needle, 4, which rides in the grooves provided in the face of the record. The element 4 may also .be said to scan the record. In actual construction the stylus 4 is one plate of a condenser of small size. The fixed plate of the condenser is spaced within unit 2 from the stylus electrode, andthe movable electrode may take the form of a metallic ribbon. The numeral 5.

1 denotes the fixed or "hot plate, and 4 the stylus attached to the movable ribbon. It is not neces- In genand "the support a is shown as being substantially L-shaped. The 'L-shaped support 8 is preferably secure several hundred I used which are different from sary to show the detai 7 Instead of using a conventional tone arm, and its finely-balanced, construction, the supporting means 3 is utilized in place thereof. This support 3 'generally'is a metallic mass which may have any desired configuration. Specifically, merely by way illustration, the shape of thin relative to its width. The lower face of .the section 8 is provided with a member l which is in i direct contact with the record-face. The member I is preferably composed of a fibrous material,

such as felt, which functions to pull the entire pickup and support along thus allowing the stylus 4 to trace the modulated grooves accurately. The felt pad I may have the shape of section 6. The

felt pad will not tend to grip the reoordface, be-

cause the weight of the support is distributed over thelarge surface of the pad. Its thickness should be such that whenthe stylus point is positioned in a groove thelower face of the pad will contact the record face at-all points.

The metallic support I can be of any metallic composition. We have-found brass or copper to be most suitable. However, the mass of thesupport should be sufficient to; act as a weight on the stylus such that proper pressure is exerted thereon. A minimum force of about iii-grams should be exerted on the stylus so as to prevent skating" along thewall of the groove. Amaximum force of about 1 ounce stylus force is sumcient to playings. The support weight, in general, should be so chosen that its vertical inertia is low so that it can follow an uneven record surface. Its horizontal inertia should be sufficiently low to minimize pressure on the groove sidewalland to avoid groove Jumping,

but not so low as-to allow low frequency vibrations to be set up. Of course, materials maybe those disclosed herein. It will be noted that, the present system has the advantage of eliminating swinging and torsional tone arm resonances, which. are practically impossible to eliminate with conventional tone arms.

The tangential motion of the support is restricted by a pair of twisted conductors 8 and 9. One end of the'conductor 8 one terminal a of a tuned link circuit. The latter consists of coil II in shunt with condenser H. The coil III has but a singleloop, since the operating frequency may be chosen from a range of 100 to, 500 megacycles (mc.). The stylus 4 is to be understood as being in electrical contact with the support 3 whereby the stylus electrode is electrically connected to terminal 8'. The sec-' the transmission lines ll are composed of fine wires. V

The ultra-high frequency vided by an oscillator circuit tube I! which acts as the oscillator oscillations are protube. The

2,874,785 s of the pickup unit inv terior, since, the last mentioned Sinnett applicationclearly discloses the constructional details. "Furthermore, since the present invention is independent bf the specific construction of the pickup unit, the details of the latter are omitted.

is connected to the support 3, while the opposite end is connected to 8 and 9 maybe a pair which comprises the 15' the circuit 20- 2l is'connected to'ground by a tube It may be a triode of circuit shown operatively connected to H3 is well known, and is employed togenerate ultra-high frequency oscillations. The resonant tank circuit comprises an inductance it which consists of a single loop. One end of the loop is connected to theplate 15, while the other end of the loop is connected to grid is through the direct current blocking condenser H. The midpoint of loop It is connected to the +3 terminal of the direct current energizing source, while the cathode is is grounded. The grid side of condenser I1 is connected to ground through grid leak resistor 19. The inductance of wire it is resonated by the distributed capacity thereof to the operating frequency of the oscillations. Other mechanical arrangements such as plates, cups, etc., may be used for the U. H.'F. (ultra high frequency) resonant circuits as may be common in U. H. F., or micro-wave work.

While a frequency of (irnc; can be used as an example, it is to be clearly understood that any other frequency in the stated megacycle range may be employed. For example, frequencies as high as 2,000 mc. may be utilized. Oscillator circuits for generating such high frequencies are known. It will be understood that the oscillator I circuit'generates the ultra-high frequency oscillations with substantiallyconstant amplitude. If a crystal, or magnetic, pickup were used, the leads 8 and 9 could go to anaudio amplifier.

There is located within the'fleld of the oscillator tank circuit H a resonant circuit which comprises a loop conductor 20 shunted by a tun- Of course, the distributed ca- Iii may be employed to resing condenser 2|.

pacity of conductor onate conductor 20. The resonant frequency of circuit.202i is chosen so that it is located above; or belowthe normal frequency of tank 40 circuit it. For example, circuit 20-2] tuned to 70% (approx.) of resonance. In other wordathe resonant circuit 20- is -'mistuned with respect to the frequency of the oscillations generated by the oscillator circuit. The circuit 4c "-48, tuned to the frequency of circuit I4, is coupled to circuit. iii-2|, and'will'transfer to g the latter any ultra-high frequency energy which existsincircuit Ill-l I. I

Since the capacity of the pickup is across the circuit l0l i, variations in the capacity magnitude of the'pickup will vary the frequency of the tuned link circuit in accordance" with the modulation sound grooves of the record- In other words the recorded sound waves are convertedinto capacity variations, and the latter are transformed into frequency variations of circuit ifll|. However, circuits l0-ll andjO-fl are in the field of the oscillatory energy radiated by the oscillator. Hence, the ultra-high frequency to energy absorbed by circuit ill-ii is modulated in accordance with the that circuit.

It will, therefore, be seen, that there is produced in circuit Iii-ll modulated ultra-high to frequency energy, and this modulation is in accordance with the sound waves which were recorded on the record.

The anode II of rectifier 30 is connected to one terminal of condenser 2|, while the, cathode 32 is connected to ground. The opposite terminal of the as type. The

may be frequency variations of v The diode rectifier 30 is 'proidded to rectify the amplitude modulated s18- voltage developed across resistor 40 may be transmitted to a following audio frequency amplifier through the coupling condenser 50.

In operation, when it is desired to play a record the operator picks up the support 3 to T change his record, and then merely places the support upon the record face as shown in the drawingin Fig.2. 'Ihestylus point is, positioned at the customary peripheral groove, and the turn table is actuated. It is to be understood that the present invention is also'applicable to records playedback from the inside to the periphery.

I It is, also, applicable to cylindrical records, or,-in

general, to any form of rotating record employing a sound groove. As the turntable revolves the record moves in the customary fashion relative to the stylus. By virtue of the restraining influence of wires'89 and the action of the pad I on the record face the pickup support 3 pulls the entire assembly. along 7 towards the axial area of the record, with the result that the stylus point traces the modulated grooves of the record accurately. Of course, the wires 89 should be 'sufliciently long to permit the support I to be displaced towards 'the innermost grooves of the record. Furthermore, there should not be developed sufllcient friction between the wires and post l2 to prevent such radial motion of the pickup support.

Support 3 will move toward the center. of the record, as shown by the dotted lines in Fig. 2, because post I2 is located in the right place; on the centerline traced between the inside and outside grooves of the record. Besides, wires 8 and 9 are of small cross section, and thus ,will not resist sidewise motion of the support. Due to the location of the supporting wires 8 and 9, the shape and location of the felt pad with respect to the stylus, and the rotation of the record, the support is maintained at all times in the correct position to properly track the sound groove. Once this position is assumed, with the record rotating, there is nothing to change it, and even if the support is twisted deliberately it will return to the correct position when released. A balance of the forces, set up by the record due to its rotation, is accomplished by properly distributing the weight of the support between the pad and the stylus.

While we have indicated and described a system for carrying ourinvention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of our invention, as set forth in the appended claims.

What we claim is:

1. In combination with a sound wave record of the disc type, a pickup device provided with a stylus adapted to ride in the record groove. and means for supporting said pickup. said supporting 'means being completely positioned on the record face and adapted to be supported by the record.

2. In combination with a sound wave record of the disc type,' a-pickup device provided with a stylus adapted to ride in the record groove, means for supporting said pickup, said supporting means being completely positioned on the record face and adapted .to be supported by the record, said supporting means being provided with a fibrous pad over at least a portion of the lower face thereof, said pad being in complete contact with the record face, means for deriving an audio voltage from the pickup output, and

conductors connecting said ing means.

3. In combination with a phonograph record adapted to be rotated about an axial point, a pickup device constructed and arranged so as to pickup to said derivm; be wholly supported on. and by said record, a

transmission line connected to said pickup device and functioning to restrain the motion thereof in a tangential direction, and a network coupled to said transmission line for amplifying the electrical energy representative of the recorded sound waves.

4. In combination with a phonograph record, means for rotating the record about a central point, a pickup device, a supporting means adapted to be supported wholly on the face of the record, said pickup device being rigidly secured to said supporting means, and a flexible conductor connected between said pickup device and a point fixedly located relative to the record for constraining the motion of the pickup supporting means to radial displacement.

5. In combination with a rotatable sound wave record, a pickup device provided with a stylus.

adapted to ride in the record groove, means for supporting said pickup, and said supporting means being completely positioned on the record face and adapted to be supported by the record.

6. In combination with a sound wave record, a pickup device provided with a stylus adapted to ride in the record groove, a metallic mass for" supporting-said pickup, said supporting mass being completely positioned on the recordface and.

adapted to be supported by the record, said sup? porting mass being provided with a fibrous pad,

and said pad being in contact with the record .face.

'7. In combination with a phonograph record adapted to be rotated about an axial point, a

pickup device constructed and arranged so as to be wholly supported on and by said record, .a transmission line connected to said pickup device and functioning to restrain the motion thereof in a radial direction, and a network coupled" the record for constraining the motion of the pickup supporting weight to radial displacement. 9. In combination with a sound-wave record of the disc type. a pickup device provided with a stylus adapted to ride in the record groove, anda metallic mass for supporting said pickup, said mass being completely positioned on the record face and adapted to be supported by the record,

and flexible meansto restrain the motion of the mass.

10. In' combination with a sound wave record of the disc type, a pickup device provided with a stylus adapted to ride in the record groove, a.

weight for supporting said pickup, said weight being completely positioned on the record face and adapted to be supported by the record, said weight being at least a portion of the lower face thereof, said provided with a fibrous pad over motion thereoi pad being in complete contact with the record face, means for derivins an audio voltage irom the pickup output, and flexible conductors conmeeting said pickup to saidderiving means.

11. In combination with a phonograph record adapted to be rotated about an axial point, a weighted pickup device constructed and arranged so as to be wholly supported on and by'said record. a flexible tron line connected to said pickup device and functioning to restrain the in a radial workco'upled to said transmission line tor-amthe recorded sound waves.

'12. In combination with means for rotating the record about point, a pickup device, tobe supported wholly c phonograph record, a central a metallic plate adapted on the race or the record.

14. In combination with a'rotatable sound rec-- with sis alcrepresentative grooves, a pickup device provided with an element adapt-" ed to ride in the record grooves, means for sup-n in operative relation to said direction, and a netplifying the electrical energy representative of said pickup device being rigidly secured to said.

and adapted to be supported by the record.

representative 0! with the record race, and a flexible conpositioned on the record race device, said supporting means ord provided p rtins said pickup record, and said supporting means being completely positioned on the record race and adaptthe area or the; being a small a fraction of the total area or the record.

with a rotatable grooved. sound wave record. a pickup device provided with ride the srooves of the ed to be supported by the' record,- supporting means for the pickup I 15. In combination an elementadapted to record, means for supportins said pickup device, said supporting means completely positioned on the record face, at least'a portion of said supporting means being provided with an element in frictional contact'with said record 'iace. i

combination withasound wave record provided with grooves,

with a needle element p of the-record, means ior supporting said pickup being. completely the record race. at least a portion a pickup device provided positioned on of said supporting means beingprovided with an and sliding contact with element in. frictional" said record face, and said'last element having an area which is a small traction oi the total area; i oitherecorda Q ""--CHESTERM.SINNE'I'I.

adapted toride the grooves 

